The present invention relates to a method for forming composite vapor-deposited films with different film compositions formed in the initial and final stages of evaporation in a continuous vacuum vapor-deposition process, and a composite vapor-deposition material suitable for use in vacuum vapor-deposition. More particularly, the present invention relates to a method for forming a composite vapor-deposited film with film compositions greatly varied as found in a light reflecting film and an optical absorption film provided on a phosphor surface in a cathode-ray tube, such as a color television picture tube, and a composite vapor-deposition material suitable for use in vacuum vapor-deposition.
The need for forming a plurality of laminated vapor-deposited films having different properties in a continuous vacuum vapor-deposition process arises. In a cathode-ray tube, such as a color television picture tube, for example, phosphors of three colors are applied in a dotted or striped pattern to the inside surface of the faceplate, with a thin-film layer having a high light reflectivity, such as aluminum, formed on the phospher-coating, that is, the surface opposite to the faceplate, so that the light going toward the inside of the CRT among visible light emitted from the phosphors is reflected by the aluminum thin-film layer to increase the amount of light reaching the front surface of the faceplate. In rear of the phosphor-coated faceplate surface disposed is a shadow mask, or an aperture mask, that acts as color selecting electrodes to control the position on the phosphor faceplate at which each of electron beams from the electron gun can strike only its intended color phosphor dot. These electrodes allow about 20% of the electron beams to pass through the shadow mask to the side of the phosphor-coated surface, while shielding the remaining 80%. The shielded 80% of the electron beams contributes to a temperature rise in the color selecting electrodes. The temperature rise causes heat radiation from the color selecting electrodes, which is concentrated to the closest phosphor-coated surface, with most of the heat reflected by an aluminum mirror backing provided on the phosphor-coated faceplate. Since the reflected heat reaches the color selecting electrodes again, the temperature rise in the electrodes is further facilitated. With the temperature rise, the color selecting electrodes may be deformed due to thermal expansion, leading to misalignment of the electron beams.
Previous efforts to cope with this have included the application of a carbon coating on the surface of an aluminum film layer provided on the phosphor surface, as disclosed in U.S. Pat. No. 3,703,401, so that radiant heat from color selecting electrodes can be absorbed by the heat absorbing effect of the carbon coating. Carbon coating, however, has to be sprayed after dissolved in a solvent, such as an organic solvent. Moreover, this spray coating must be carried out separately from the process of vacuum vapor-deposition of aluminum onto the phosphor surface. This makes the process complex and troublesome, and continuous operation impossible.
When carbon or chromium, both having a radiant-heat absorbing property, is vacuum vapor-deposited together with aluminum having a high light reflectivity, a composite vapor-deposited film having an aluminum-rich composition formed in the initial stage of the vapor-deposition and a carbon- or chromium-rich composition formed in the final stage can be expected due to a difference in vapor pressure between aluminum and carbon or chromium. The aluminum-rich composition formed in the initial stage, however, has a low light reflectivity due to the high content of carbon or chromium. The carbon- or chromium-rich composition formed in the final stage, on the other hand, contains a large amount of aluminum, leading to a meager level of radiant-heat absorption.
To cope with this, a vapor-deposited film having a double-layer construction consisting of entirely different compositions can be obtained by first forming a vapor-deposited film by placing an aluminum block as an initial vapor-deposition material on an evaporation tray, and then continuing evaporation by placing an vapor-deposition material, such as carbon or chromium, that is different from the initial vapor-deposition material on the evaporation tray. This, however, involves two separate vapor-deposition procedures.
It is therefore an object of the present invention to provide a method for forming a composite vapor-deposited film having different film compositions formed in the initial and final state of vapor-deposition in a continuous vacuum vapor-deposition process.
It is another object of the present invention to provide a composite vapor-deposition material suitable for forming a composite vapor-deposited film having different film compositions formed in the initial and final state of vapor-deposition.
It is a further object of the present invention to provide an elongated composite vapor-deposition material having metals, alloys, their oxides, or their mixtures, that are relatively hard to elongate.
It is still a further object of the present invention to provide a composite vapor-deposition material that can be automatically fed to a vacuum vapor-deposition apparatus with ease.
It is still a further object of the present invention to provide a method for manufacturing a composite vapor-deposition material.
Accordingly, the method for forming a composite vapor-deposited film having different film compositions formed in the initial and final stages of vapor-deposition according to the present invention involves heating under reduced pressure a composite vapor-deposition material having a high vapor-pressure metal body, and a low vapor-pressure metal held in the core region of the body, and then vaporizing the high vapor-pressure metal and the low vapor-pressure metal to deposit them on a substrate being deposited.
In the present specification, high vapor-pressure metals are defined as metals that vaporize at relatively low temperatures, and low vapor-pressure metals are defined as metals that do not vaporize unless heated to relatively high temperatures, when dissimilar metals are heated in the same degree of vacuum.
The low vapor-pressure metal may be a powder dispersed and held by the high vapor-pressure metal powder in the core region of a high vapor-pressure metal body in a composite vapor-deposition material. The high vapor-pressure metal body should preferably be of the same metal as used for the high vapor-pressure metal powder, and more preferably be aluminum or its alloy. The high vapor-pressure metal should preferably have a higher ductility than the low vapor-pressure metal. The low vapor-pressure metal powder can be at least any one element selected from the group consisting of carbon, silicon, chromium, nickel, iron, cobalt, titanium, rhenium, tungsten and vanadium.
The low vapor-pressure metal may be a bulk covered by an envelope of a metal that has a higher vapor pressure and higher ductility in a composite vapor-deposition material. The high vapor-pressure metal should preferably be aluminum or its alloy, while the low vapor-pressure bulk metal should preferably be at least any one element selected from the group consisting of beryllium, tin, gold, iron, cobalt, nickel, titanium, platinum, rhodium, niobium, tantalum, rhenium and tungsten.
This composite vapor-deposition material may have a foil or layer of a lower vapor-pressure metal, which should preferably be niobium, tantalum, rhenium or tungsten, enclosing the core region.
The composite vapor-deposition material according to the present invention may have a composite construction in which a high vapor-pressure metal envelope having a cavity inside thereof, and a mixture of a high vapor-pressure metal and a low vapor-pressure metal packed into the cavity are integrally cold worked so as to cause the low vapor-pressure metal powder to be dispersed and held by the high vapor-pressure metal powder in the core region of the high vapor-pressure metal body.
The method for manufacturing the composite vapor-deposition material according to the present invention has a process of obtaining a composite construction in which the low vapor-pressure metal powder is dispersed in the core region of the envelope by mixing a high vapor-pressure metal powder with a lower vapor-pressure metal powder, packing the mixture powder into a high vapor-pressure metal envelope, and reducing the diameter of the envelope by cold working. The high vapor-pressure metal used here should preferably be aluminum or an aluminum alloy. The cold working should preferably be cold wire drawing. The total reduction ratio in cold wire drawing should preferably be not less than 75%. The angle of repose of the mixture powder should preferably be not more than 45 degrees.
In the method for manufacturing the composite vapor-deposition material according to the present invention, ends, including closed ends, of a plurality of cold-drawn aluminum or aluminum-alloy envelopes can be cut and discarded, and the envelopes thus obtained can be connected to each other at the cut portions by welding for further cold wire drawing.